The present invention is directed to a mechanically firm glued connection between surfaces and a method for producing the connection.
A method for producing mechanically firm glued connections between surfaces, with each of the surfaces to be connected having at least one surface region that extends over the surface and comprises a roughness with a small peak-to-valley height t and is provided for the production of a glued connection having the steps of setting the surface regions having the small peak-to-valley height opposite one another with the intermediate space between these surfaces extending in a planar direction over the surface and having a small average thickness, providing a hardenable glue having a low viscosity and then hardening the glue contained in the intermediate space to essentially maintain the small average thickness of the intermediate space was disclosed, for example, in Elektronik Produktion und Pruftechnik, May 1989, pages 40-44. In this known method, the surface regions of the surfaces to be connected, which regions extend over a surface and are provided for the production of a glued connection, comprise a small peakto-valley height of from 0.5 .mu.m to about 2 .mu.m. The connecting glue layer, consisting of a hardenable glue, is provided in the intermediate space between the surface regions comprising a thickness of 0.5 .mu.m to 1 .mu.m.
In an embodiment of this known method, the surface regions provided for the production of the glued connection are first placed together, and the low-viscosity glue consisting of a cyanoacrylate is subsequently brought into the intermediate space by means of the surface tension.
In another embodiment of this invention, a glue drop made of epoxy is first deposited on one of the surfaces to be connected using an extruder, and the other surface is then applied with a pressure of 30 cN/mm.sup.2. With this known method, it is possible to produce conductive glued connections with glues that are non-filled, for example glues which are electrically insulating.
U.S. Pat. No. 4,817,277, whose disclosure is incorporated herein by reference thereto and which claims priority from the same German Application as European 0 237 114, discloses a method for producing an electrically conductive glued connection between electrically conductive parts, whose surfaces to be glued likewise comprise a surface roughness with a peak-to-valley height. In this known method, the surfaces to be connected are, respectively, provided with a layer of at least one transition element of a first and/or second transition series of the periodic table of the elements, which provides a peak-to-valley height in the .mu.m range. For the production of the glued connection, an electrically non-conductive glue is used in such a quantity that the raised regions of the transition element layers still achieve contact with one another. The peak-to-valley heights used in this method amount to a few 0.1 .mu.m, with the use of copper as a transition element, and are larger, for example around 1 .mu.m, given the use of other transition elements. A desired peak-to-valley height can be achieved using an ion etching process. The glue is deposited on one of the surfaces to be connected by a thin brushing, and can consist, among other things, of an adhesive paint based on the cyanoacrylate, epoxy resin or polyester. The transition resistance of the glued connections produced according to this method is in the range of 3 to 9 m.OMEGA./mm.sup.2 of the contact surface given simultaneous mechanical and thermal loading.
To produce an electrically conductive glued connection between an electronic or, respectively, a microelectronic module and a substrate element, the Japanese company Matsushita uses a gluing method with an electrically insulating glue, in which the surface of the module that is to be connected with the surface of the substrate element comprises, for example, humps or bumps made of gold with a height of at least 3 .mu.m and a surface of 251 .mu.m, and the humps or bumps are arranged with a 10 .mu.m grid.
For the production of the glued connection, the surface of the substrate element provided with the terminals is coated with an electrically insulating glue that hardens in a UV light and that shrinks when it hardens.
The surface of the module provided with the humps and the surface of the substrate element provided with the terminals are positioned opposite one another in such a way that each hump of the module respectively lies opposite a terminal of the substrate element.
After this, the two surfaces are pressed against one another with a pressure, for example 1.5 to 3 cN/25 .mu.m.sup.2 and are exposed to ultraviolet light, for example for 3 seconds at 1 mW/cm.sup.2.
By means of the shrinkage tension that occurs during the hardening of the glue, the humps or bumps and terminals lying opposite one another are permanently pressed against one another so that no electrically effective barrier layer arises (transition resistance 18 m.OMEGA.). A high reliability also occurs with respect to shock, for example thermal cycling between -55.degree. C. and 125.degree. C. with 1000 cycles, a temperature storage of 1000 hours at 125.degree. C. and a humid heat at 85.degree. C. with 85% humidity for 100 hours.
Glass, ceramic and hard substrate elements can be used as the substrate elements.
With this method, it is possible to realize LED arrays with IC control, comprising 7 .mu.m-high humps arranged in a grid of 63.5 .mu.m and 100 .mu.m.